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← JEE Advanced 2017 · Paper 2
PhysicsSingle correct+3 / -1Question 6 of 54

JEE Advanced 2017 · Paper 2, Physics question 6

A rocket is launched normal to the surface of the Earth, away from the Sun, along the line joining the Sun and the Earth. The Sun is 3×1053 \times 10^5 times heavier than the Earth and is at a distance 2.5×1042.5 \times 10^4 times larger than the radius of the Earth. The escape velocity from Earth’s gravitational field is ve=11.2 km s−1v_e = 11.2\ \mathrm{km\,s^{-1}}. The minimum initial velocity (vS)(v_S) required for the rocket to be able to leave the Sun-Earth system is closest to

(Ignore the rotation and revolution of the Earth and the presence of any other planet)

Choose one option
Answer and worked solution

Official answer: B

Energy needed. To escape both bodies from Earth's surface (on the far side from the Sun):
12vS2=GMeRe+GMsr,GMsr=GMeRe⋅3×1052.5×104=12GMeRe.\tfrac12v_S^2=\frac{GM_e}{R_e}+\frac{GM_s}r,\qquad\frac{GM_s}r=\frac{GM_e}{R_e}\cdot\frac{3\times10^5}{2.5\times10^4}=12\frac{GM_e}{R_e}.

Solve.
vS2=2GMeRe(1+12)=13ve2  ⟹  vS=13×11.2≈40.4 km s−1,v_S^2=\frac{2GM_e}{R_e}(1+12)=13v_e^2\implies v_S=\sqrt{13}\times11.2\approx40.4\ \mathrm{km\,s^{-1}},
which is closest to 42.

(B)